E additional

Hunt Hypothesis

This rule identifies suspicious email content, such as phishing attempts or malicious attachments, that may have bypassed standard filters. Proactively hunting for these indicators in Azure Sentinel allows the SOC team to detect early-stage social engineering campaigns and isolate compromised endpoints before lateral movement occurs.

YARA Rule

rule E_additional: PEiD
{
    strings:
        $a = { 55 8B EC B8 ?? ?? ?? ?? BB ?? ?? ?? ?? 50 E8 00 00 00 00 58 2D A7 1A 00 00 B9 6C 1A 00 00 BA 20 1B 00 00 BE 00 10 00 00 BF B0 53 00 00 BD EC 1A 00 00 03 E8 81 75 00 ?? ?? ?? ?? 81 75 04 ?? ?? ?? ?? 81 75 08 ?? ?? ?? ?? 81 75 0C ?? ?? ?? ?? 81 75 10 }
    condition:
        $a at pe.entry_point

}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Legitimate Automated Reporting with Embedded Scripts: Business Intelligence tools like Tableau or Power BI often send daily summary emails containing .html attachments or embedded JavaScript for interactive charts. If the YARA rule flags generic script patterns or specific MIME types, these legitimate reports will trigger alerts.

  • Filter/Exclusion: Exclude emails from verified senders in the bi-reports@company.com domain or whitelist attachments with specific filenames (e.g., daily_kpi_report.html) when the sender is a known service account.

• IT Asset Management Notifications: Systems like ServiceNow or Jira frequently send automated notifications that include attached PDFs or HTML snippets for change requests or ticket updates. These emails may contain standard HTML structures or base64-encoded content that matches broad “phishing” heuristics in the rule.

  • Filter/Exclusion: Create a rule exclusion for senders matching it-automation@company.com or jira@company.com and allow attachments with extensions .pdf or .html if the subject line contains standard prefixes like [Ticket] or [Change].

• HR Onboarding and Offboarding Packets: The HR team uses Workday or SAP SuccessFactors to send new hire welcome packets or offboarding checklists. These emails often include multiple attachments (PDFs, DOCX) and may use complex HTML layouts for branding. If the rule detects “multiple attachments” or “complex HTML structure” as suspicious, these routine HR communications will be flagged.

  • Filter/Exclusion: Whitelist senders from hr-ops@company.com and allow emails with subject lines containing keywords like “Welcome,” “Onboarding,” or “Offboarding” regardless of attachment count or type.

• Vendor Invoice Processing: Accounts Payable receives automated invoices from vendors via **